A gas leak detecting device of a heater pipe and a gas leak detecting method of a heater pipe, which are able to reliably detect a leak of gas from a heater pipe in which a fine hole is formed. A gas leak detecting device of a heater pipe, which is provided with an inside pipe housing a heater element and an outside pipe sealed surrounding the inside pipe and which is adjusted by a pressure adjustment mechanism in gas pressure in a space between the outside pipe and the inside pipe to a predetermined pressure value. The gas leak detecting device includes a gas flow resistance part, a pressure detection unit, and a leak judging device that judges whether gas is leaking from the heater pipe based on a detected pressure value obtained by the pressure detection unit.